There are a number of U.S. patents that disclose electronic apparatus for printing indicia on labels, some of which are described in U.S. Pat. No. 4,440,248, Teraoka; U.S. Pat. No. 4,501,224, Shibayama; U.S. Pat. No. 4,630,538, Cushing; and U.S. Pat. No. 4,655,129, Wirth et al.
The electronic machines for printing labels of the type disclosed above all include the same general combination of elements, a print head, means for feeding labeling media to be printed past the print head, a microprocessor, a read only memory programmed with appropriate instructions to operate the microprocessor, a random access memory, a keyboard with letter, number, and function keys for the entry of alphanumeric information concerning the indicia to be printed, and a visual display such as a LED/LCD unit to assist the operator in using the machine.
The labeling media comprises a roll of pressure sensitive tape (continuous media or die cut labels)that is attached to a continuous roll of release liner. The labeling media is fed through the printer and legends are printed on the tape. Labels are formed using the continuous tape by cutting the media after the legends are printed thereon. The labels are then removed from the release liner and attached to the objects needing identification. As there are many types of label applications, there are many combinations of tape and release liners that provide labels of varying sizes, colors, formats, and environmental resistance.
A particular type of print head employs thermal transfer printing technology. Thermal transfer printing uses a heat generating print head to transfer a colored coating containing wax, carbon black, or the like, from a thermal transfer ribbon to a labeling media. By using digital technology, characters are formed by energizing a sequence of pixels on the print head which in turn melt the coating on the ribbon transferring the image to the labeling media.
In a known thermal transfer printer such as a label printer, labeling media is fed by a platen roller simultaneously with a ribbon feed roller feeding an ink transfer ribbon. While the labeling media driven by the platen roller runs between the print head and the rotating platen roller, the transfer ribbon is passed between the print head and the platen roller by rotating the ribbon feed roller. As a result, the labeling media and the transfer ribbon pass together in overlay relationship between the print head and the platen roller.
Many of prior art thermal printers disclosed above have ink ribbons containing more than one color for printing multi-colored indicia on the label. These colors are composed of various substances which are optimally printed at different specific platen pressure (i.e., pressure exerted on the platen by the print head). Prior art printers have a single fixed platen pressure, or multiple fixed pressures requiring intervention by the user to change. Even with the multiple fixed pressure printer variety, the desired pressure may lie between the discrete available settings, resulting in printing the color at a less than optimal pressure.